M&S says

Bedsheets need not be 'make do and mend', with this luxurious Supima® cotton fitted sheet, ultimate comfort and indulgent rest is offered in spades. Boasting a myriad of properties that make this bedsheet incredibly soft on the skin, the name Supima® is so special that just 1% of the world’s cotton is permitted to carry its name. The modern design, sleek nature, and rich sheen finish of this supersoft fitted sheet creates a truly wonderful experience in sleep comfort that is sure to match any room’s aesthetic design.